I use a Dakine Fusion kiteboarding seat harness. It offers better support than the Hobie seat harness when you're out on the wire and is better made in my humble opinion, but the tradeoff is the Dakine isn't quite as comfortable when you're sitting on the tramp for long periods. Poke around YouTube - there are plenty of reviews out there. Dakine comes with a "hammer head" spreader bar that works well with "can't miss" style trap handles. If you prefer dog bones, Dakine's bar might not be a good option as I'm not sure it would fit.

My suggestion would be to shop around and see what fits your body and sailing style and falls within your budget. And look for end-of-year close-outs (I saved about $80 on my Dakine by purchasing the previous year's model). In addition to Hobie and Dakine, Magic Marine and Gill also make good harnesses but they aren't cheap. I've tried the MM shoulder style and its really nice. I havent tried or seen Aquata but many of the full shoulder/leg models Optikid linked look like they might be overkill for weekend warrior types like me.

I just ordered the Ronstan Racing Harness after debating over the prices. What cinched the deal for me was reading the reviews. It was $200, but from what I read, reviewers seemed to agree that it was well worth the extra $50 for the amount of back support it provides. I'm looking forward to trying it out.